There nothing else I found on UE4 side that hurted the determinism on my test project besides the mentioned things. I compiled and debugged physx code a bit to find out where it messed up with the transforms when you set them but there were just too many places it could have happened (physx does many math operations for the tranform before it gets stored anywhere internally) and there could also be some other internal physx cache scenario that caused things to get altered too. I’m now talking about not being able to reset the transform to exact same value it was between physics steps without it starting to drift slightly. This is probably not huge issue but more like something to keep in mind if you wonder when results are not 1:1.
All in all, just running physx at fixed timesteps guarantees that simulation itself runs the physics equations the same way so you’ll not get physics objects that move faster on other clients (like could happen on variable timesteps).